Currently, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, and the like are used as commercial secondary batteries. Among them, lithium secondary batteries have little to no memory effect in comparison with nickel-based secondary batteries, and thus lithium secondary batteries are gaining a lot of attention for their advantages of free charging or discharging, low self-discharging, and high energy density.
A lithium secondary battery generally uses lithium oxide and carbonaceous material as a positive electrode active material and negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate respectively coated with the positive electrode active material and the negative electrode active material are disposed with a separator being interposed between them, and an exterior, namely a battery case, which seals and accommodates the electrode assembly together with an electrolyte.
Generally, a lithium secondary battery may be classified into a can-type secondary battery where the electrode assembly is included in a metal can and a pouch-type battery where the electrode assembly is included in a pouch of an aluminum laminate sheet, depending on the shape of the exterior.
Recently, secondary batteries are widely used in middle- or large-sized devices like vehicles and power storage devices as well as small-sized devices like portable electronic appliance. When used in such middle- or large-sized devices, a plurality of secondary batteries are electrically connected in large numbers to increase the capacity and output. Especially, in such middle- or large-sized devices, pouch-type secondary batteries are usually employed because they can easily be stacked.
However, the pouch-type secondary battery does not give great mechanical rigidity since it is packaged with a battery pack generally made of a laminate sheet of aluminum and polymer resin. Therefore, when a battery module including a plurality of pouch-type secondary batteries is configured, frames are frequently used to protect the secondary batteries against external impacts, prevent the secondary batteries from moving and facilitate easier stacking.
The frame may also be called with various terms such as a cartridge. The frame generally has a rectangular plate shape with a hollow center, and at this time, four side portions of the frame are configured to surround an outer circumference of the pouch-type secondary battery. In addition, a plurality of frames is stacked to configure a battery module, and a secondary battery may be located in an empty space created by stacking frames.
Meanwhile, when a plurality of secondary batteries is assembled using a plurality of frames as described above, a cooling fin having a plate shape may be interposed between secondary batteries. A secondary battery may be used under a high-temperature environment, for example in summer, and the secondary battery may generate in itself. At this time, if a plurality of secondary batteries is stacked, the temperature of the secondary batteries may be increased further, and if the temperature rises over a suitable level, the performance of the secondary batteries may be deteriorated, and in severe cases, the secondary batteries may be fired or exploded. Therefore, when a battery module is configured, a cooling fin is frequently interposed between secondary batteries so that the cooling fin prevents the temperature of the secondary batteries from rising.
If a battery module includes a plate-like cooling fin, namely a cooling plate, interposed between secondary batteries, the secondary batteries may be cooled in various ways. Representatively, an air-cooling method for allowing an external air to flow around the cooling plate and thus lowering a temperature of secondary batteries by exchanging heat between the cooling plate and the air is widely used. If a battery module uses the air-cooling method to cool secondary batteries, a cooling flow path should be ensured around the cooling plate, and the cooling flow path should be connected to a duct so that air may flow into or out of the battery module.
However, if the battery module is configured as above, a gas generated from a secondary battery may flow out through the cooling flow path and the duct. In other words, a pouch-type secondary battery may generate a gas in use, and the gas may contain ingredients harmful to a human body. However, if the harmful gas generated from a secondary battery penetrates into the cooling flow path, the penetrating gas may be discharged out through the duct, and a battery user may inhale the discharged harmful gas. In particular, in case of a hybrid vehicle or an electric vehicle, a middle- or large-sized battery pack including numerous secondary batteries is mounted, and thus gas may be more likely to be discharged from the secondary batteries. In addition, if a harmful gas is discharged from such a battery pack for a vehicle and flows into the duct, a vehicle driver may inhale the harmful gas flowing into the duct, which may harm the driver and also deteriorate driving ability of the driver to cause an accident.